Can I share Steam updates between computers?

Solution 1:

In my own experience you can simple copy paste the entire Steam/Valve folder and run it from it's new destination.

Hence, yes you can just copy the entire game's folder with the updates to the other computer

And I just stumbled upon a Super User question about this. Quoting John T:

I do this all the time it is fine to do. Any files that do not match are usually re-downloaded from Steam, hence why it will still update a bit after a fresh copy. If you do not want all the sounds and maps which take up a lot of space, you can simply take the .gcf files for each game from Program Files/Steam/SteamApps, these are the biggest files in the update which will save the most time.

Steam also has a "Backup" feature you can use. The files it creates can be moved from PC to PC and restored on any one.

Solution 2:

Another option is to backup through steam on one machine and then restore the backup to the 2nd machine.